In the packaging of integrated circuits, device dies may be bonded to package components such as additional device dies, interposers, package substrates, printed circuit boards (PCBs), or the like. Solder balls are commonly used for bonding the device dies to the package components. In a typical bonding process, solder flux is applied on the surfaces of bonding features, followed by a reflow to melt solder.
With the increasing down-scaling of integrated circuits, the pitches of the solder balls become increasingly smaller. For example, the pitches of solder balls/bumps may be as small as 140 μm for solder ball/bump arrays, or even smaller for peripheral solder ball/bumps that are located close to the peripheral of the device dies. This causes difficulty for package assembly cleaning processes. For example, after the reflow of solder ball/bumps in a package assembly, the flux residue remaining in the package assembly needs to be removed. However, when the pitches of the solder ball/bumps become small, the gaps between the solder balls are also small. Therefore, it is difficult for the solvent and water that are used in the cleaning process to flow into and out of the gaps between the solder balls.
In addition, in the conventional package assembly cleaning processes, solvents were sprayed onto the package assemblies. With such a method, the efficiency of the package assembly cleaning process also becomes lower with the reduction in the pitches. It is not feasible to increase the cleaning efficiency by increasing the pressure of the sprayed solvent, since the increased pressure may cause damage to the dies, which may include low-k dielectric layers therein, and hence are prone to the damage of the increased pressure.